A color diffusion transfer photographic process using an azo dye image forming compound which provides an azo dye having diffusibility different from that of the image forming compound per se as a result of development under a basic condition has hitherto well known in the art. Image forming compounds which release cyan dyes include, for example, those described in U.S. Pat. Nos. 3,942,987, 4,013,635, 4,273,708 and 4,268,625.
These compounds described in the above described patents have a nitro group at the p-position to the azo group. However, it has been found that there is a problem in that the nitro group is subjected to reduction to cause discoloration during the development processing. Further, azo dyes having a nitro group generally have a light reducing property and color images formed therefrom are poor in light fastness.
Moreover, when the image forming compound is incorporated into a layer containing a light-sensitive silver halide emulsion, a phenomenon of inhibiting development of the silver halide may be observed. It is considered that the reason for the phenomenon is also based on the nitro group.
In JP-A-53-66227 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), cyan azo dye image forming compounds having a trifluoromethanesulfonyl group at the p-position to the azo group are described. However, the compounds are troublesome in view of synthesis and environmental pollution, since they contains fluorine atoms. It is also desired to further improve clearness of hue and diffusibility of a dye released. In British Patent 1,490,248 and JP-A-55-40402, magenta azo dye image forming compounds comprising diazo components having two or more alkylsulfonyl groups are described. These compounds, however, have absorption in a short wavelength region and can not be used for cyan dye image forming compounds because the 2-position of the naphthol is unsubstituted or substituted with an electron withdrawing group in any of these compounds.
Recently, novel cyan azo dye image forming compounds obtained by an azo coupling reaction of diazo components having neither a nitro group nor a trifluoromethanesulfonyl group with 2-acylamino-1-naphthols have been proposed in JP-A-60-93434, JP-A-60-87134 and JP-A-60-257579. Although, the image forming compounds descried in these patents are useful as cyan dyes in comparison with conventionally known compounds, they are insufficient in color reproducibility since their color are light. Also, a large amount of the image forming compounds is necessary in order to obtain a good gray balance.
In order to solve the above described problems, azo dyes are proposed in JP-A-3-114042 and JP-A-7-219180. However, further improvement has been desired with respect to hue and light fastness.
Making an attempt to improve hue and light fastness, heterylazo dyes are developed by replacing aniline diazo components with heterocyclic diazo components as described, for example, in JP-A-60-14243, JP-A-60-140240, JP-A-62-257151, JP-A-61-44301 and U.S. Patent 5,716,754. However, these dyes are still insufficient in hue and light-fastness. Among them condensed ring isothiazolylazo dyes including typically benzisothiazolylazo dyes as described in JP-A-60-14243 and U.S. Pat. No. 5,716,754 are noticeable since they have the characteristic of absorbing longer wavelength light. However, since the naphthol derivatives which are coupler components are inappropriately selected in the compounds described in JP-A-60-14243, and since the condensed ring isothiazole derivatives which are diazo components are inappropriately selected in the compounds described in U.S. Pat. No. 5,716,754, these dyes are not preferable in color reproducibility, can not provide a good gray balance, and have insufficient light fastness. Moreover, both of these compounds have problems in that sensitivity is decreased and in that a sufficient image density can not be obtained, since they interact with silver.
As described above, cyan dyes obtained from conventionally known cyan azo dye image forming compounds have neither preferred hue nor sufficient stability to light.